Updated March 9, 16
LLIN Care and Repair Abstracts
Table of Contents
1
Maintenance of Insecticide Treated Nets ......................................................................... 2
1.1 An Observational Study of Material Durability of Three World Health OrganizationRecommended Long-Lasting Insecticidal Nets in Eastern Chad.......................................................................... 2
1.2 A stitch in time: a cross-sectional survey looking at long lasting insecticide-treated bed net
ownership, utilization and attrition in SNNPR, Ethiopia. ....................................................................................... 2
1.3 Loss of Household Protection from Use of Insecticide-Treated Nets against PyrethroidResistant Mosquitoes, Benin. .............................................................................................................................................. 3
1.4 The efficacy and physical condition of olyset insecticide-treated nets after 5 years use in rural
Lao PDR. ...................................................................................................................................................................................... 4
1.5 Which nets are being used: factors associated with mosquito net use in Amhara, Oromia and
Southern Nations, Nationalities and Peoples' Regions of Ethiopia..................................................................... 4
1.6 How much does malaria vector control quality matter: the epidemiological impact of holed
nets and inadequate indoor residual spraying............................................................................................................ 5
1.7 Factors associated with mosquito net use by individuals in households owning nets in
Ethiopia........................................................................................................................................................................................ 6
1.8 Mosquito nets in a rural area of Western Kenya: ownership, use and quality. .................................. 6
1.9 Determining and addressing obstacles to the effective use of long-lasting insecticideimpregnated nets in rural Tanzania ................................................................................................................................ 7
1.10 Culturally compelling strategies for behaviour change: a social ecology model and case study
in malaria prevention. ........................................................................................................................................................... 8
1.11 Maintenance behaviour and long-lasting insecticide-treated nets (LLITNs) previously
introduced into Bourapar district, Khammouane province, Lao PDR. .............................................................. 8
1.12 Field issues related to effectiveness of insecticide-treated nets in Tanzania. ................................. 9
2
Evaluation of Nets After a Period of Time ....................................................................... 10
2.1 Evidence for a useful life of more than three years for a polyester-based long-lasting
insecticidal mosquito net in Western Uganda. .......................................................................................................... 10
2.2 Evaluation of Interceptor long-lasting insecticidal nets in eight communities in Liberia........... 10
2.3 Loss of protection with insecticide-treated nets against pyrethroid-resistant Culex
quinquefasciatus mosquitoes once nets become holed: an experimental hut study. ............................... 11
2.4 An experimental hut evaluation of Olyset® nets against anopheline mosquitoes after seven
years use in Tanzanian villages ....................................................................................................................................... 12
2.5 Evaluation of long-lasting insecticidal nets after 2 years of household use. ..................................... 12
2.6 Evaluation of Olyset insecticide-treated nets distributed seven years previously in Tanzania.
13
3
Wash Resistance ............................................................................................................ 14
3.1 Wash resistance and efficacy of three long-lasting insecticidal nets assessed from bioassays on
Anopheles culicifacies and Anopheles stephensi. .................................................................................................... 14
3.2 Evaluation of the wash resistance of three types of manufactured insecticidal nets in
comparison to conventionally treated nets. ............................................................................................................... 14
3.3 Wash resistance of PermaNets in comparison to hand-treated nets. .................................................. 15
3.4 Evaluation of the effects of repeated hand washing, sunlight, smoke and dirt on the
persistence of deltamethrin on insecticide-treated nets. ..................................................................................... 15
Updated March 9, 16
3.5 A randomized and controlled comparison of the wash-resistances and insecticidal efficacies of
four types of deltamethrin-treated nets, over a 6-month period of domestic use with washing every
2 weeks, in a rural area of Iran. ....................................................................................................................................... 16
3.6 Multi-country field trials comparing wash-resistance of PermaNet and conventional
insecticide-treated nets against anopheline and culicine mosquitoes. ........................................................... 16
3.7 Laboratory wash resistance of long-lasting insecticidal nets.................................................................. 17
3.8 Experimental hut comparisons of nets treated with carbamate or pyrethroid insecticides,
washed or unwashed, against pyrethroid-resistant mosquitoes. ..................................................................... 18
1 Maintenance of Insecticide Treated Nets
1.1 An Observational Study of Material Durability of Three World Health
Organization-Recommended Long-Lasting Insecticidal Nets in Eastern Chad.
A total of 876 nets (229 Interceptor(®), 363 Olyset(®), and 284 PermaNet(®)) were collected 14
months post-distribution of long-lasting insecticidal nets (LLINs) from 811 households of
internally displaced and host communities in Dar Sila District in eastern Chad to examine their
physical condition. Holes were recorded by using three hole categories (average diameter = 2,
3.5, and 15 cm) and a Proportionate Hole Index (pHI). A total of 69.5% were in poor or very
poor condition. There was no significant difference in the performance between the polyester
75 denier LLINs, but they had 4.22 times the odds of having a pHI ≥ 175 (poor or very poor
condition) than polyethylene 150 denier LLINs; and 39.2% were unserviceable (pHI ≥ 300)
compared with only 7.7% of the polyethylene LLINs. These results provide the first comparative
data on LLIN material durability to guide procurement and replacement practice, and to inform
urgently needed changes in LLIN international minimum specifications and product standards.
Allan R, O'Reilly L, Gilbos V, Kilian A. An Observational Study of Material Durability of Three
World Health Organization-Recommended Long-Lasting Insecticidal Nets in Eastern Chad. Am
J Trop Med Hyg 2012,
1.2 A stitch in time: a cross-sectional survey looking at long lasting insecticidetreated bed net ownership, utilization and attrition in SNNPR, Ethiopia.
ABSTRACT: BACKGROUND: Since 2002/03, an estimated 4.7 million nets have been distributed
in the Southern Nations, Nationalities and Peoples Region (SNNPR) among an at risk population
of approximately 10 million people. Evidence from the region suggests that large-scale net
ownership rapidly increased over a relatively short period of time. However, little is known
about how coverage is being maintained given that the last mass distribution was in 2006/2007.
This study sought to determine the status of current net ownership, utilization and rate of long
Updated March 9, 16
lasting insecticide-treated nets (LLIN) loss in the previous three years in the context of planning
for future net distribution to try to achieve sustainable universal coverage. METHODS: A total of
750 household respondents were interviewed across malarious, rural kebeles of SNNPR.
Households were randomly selected following a two-stage cluster sampling design where
kebeles were defined as clusters. Kebeles were chosen using proportional population sampling
(PPS), and 25 households within 30 kebeles randomly chosen. RESULTS: Approximately 67.5%
(95%CI: 64.1-70.8) of households currently owned at least one net. An estimated 31.0% (95%CI
27.9-34.4) of all nets owned in the previous three years had been discarded by owners, the
majority of whom considered the nets too torn, old or dirty (79.9%: 95%CI 75.8-84.0).
Households reported that one-third of nets (33.7%) were less than one year old when they
were discarded. The majority (58.8%) of currently owned nets had 'good' structural integrity
according to a proportionate Hole Index. Nearly two-thirds of households (60.6%) reported
using their nets the previous night. The overriding reason for not using nets was that they were
too torn (45.7%, 95% CI 39.1-50.7). Yet, few households are making repairs to their nets (3.7%,
95% CI: 2.4-5.1). CONCLUSIONS: Results suggest that the life span of nets may be shorter than
previously thought, with little maintenance by their owners. With the global move towards
malaria elimination it makes sense to aim for sustained high coverage of LLINs. However, in the
current economic climate, it also makes sense to hark back to simple tools and messages on the
importance of careful net maintenance, which could increase their lifespans.
Batisso E, Habte T, Tesfaye G, Getachew D, Tekalegne A, Kilian A, Mpeka B, Lynch C. A stitch in
time: a cross-sectional survey looking at long lasting insecticide-treated bed net ownership,
utilization and attrition in SNNPR, Ethiopia. Malar J 2012, 11:183.
1.3 Loss of Household Protection from Use of Insecticide-Treated Nets against
Pyrethroid-Resistant Mosquitoes, Benin.
Pyrethroid resistance is becoming widespread in Anopheles gambiae mosquitoes, coinciding
with expanded use of insecticide-treated nets (ITNs) throughout Africa. To investigate whether
nets in use are still protective, we conducted household trials in northern and southern Benin,
where An. gambiae mosquitoes are susceptible and resistant, respectively, to pyrethroids.
Rooms were fitted with window traps and monitored for mosquito biting and survival rates
before and after the nets were treated with pyrethroid. Sleeping under an ITN in the location
with resistant mosquitoes was no more protective than sleeping under an untreated net,
regardless of its physical condition. By contrast, sleeping under an ITN in the location with
susceptible mosquitoes decreased the odds of biting by 66%. ITNs provide little or no
protection once the mosquitoes become resistant and the netting acquires holes. Resistance
seriously threatens malaria control strategies based on ITN
Asidi A, N'guessan R, Akogbeto M, Curtis C, Rowland M. Loss of Household Protection from Use
of Insecticide-Treated Nets against Pyrethroid-Resistant Mosquitoes, Benin. Emerg Infect Dis
2012, 18:1101-6.
Updated March 9, 16
1.4 The efficacy and physical condition of olyset insecticide-treated nets after 5 years
use in rural Lao PDR.
We assessed the insecticidal efficacy of Olyset nets after 5 years of use in rural villages of Lao
PDR and evaluated the relationship between the physical condition of the nets and their
insecticidal effect. Our results showed that most of the Olyset nets remained effective after 5
years of use; however, there was no significant relationship between the physical condition of
the nets (ie, presence of holes, level of stains) and the insecticidal effect. The presence of large
holes in polyester nets compared to the Olyset nets suggest the Olyset nets are stronger;
however, nearly half of Olyset nets had small holes or had been previously repaired.
Interestingly, the insecticide concentration and knockdown (KD) rate for 3 stored nets was low
compared to the other nets routinely used in the house. To maintain the effectiveness of Olyset
nets in rural villages of Lao PDR and other areas, residents should be advised to repair and store
the nets appropriately and avoid exposure to high temperatures and direct sunlight for long
periods.
Tsuzuki A, Khamlome B, Kawada H, Eto H, Phompida S, Takagi M. The efficacy and physical
condition of olyset insecticide-treated nets after 5 years use in rural Lao PDR. Southeast Asian
J Trop Med Public Health 2011, 42:268-73.
1.5 Which nets are being used: factors associated with mosquito net use in Amhara,
Oromia and Southern Nations, Nationalities and Peoples' Regions of Ethiopia.
ABSTRACT: BACKGROUND: There has been recent large scale-up of malaria control
interventions in Ethiopia where transmission is unstable. While household ownership of longlasting insecticidal nets (LLIN) has increased greatly, there are concerns about inadequate net
use. This study aimed to investigate factors associated with net use at two time points, before
and after mass distribution of nets. METHODS: Two cross sectional surveys were carried out in
2006 and 2007 in Amhara, Oromia and SNNP regions. The latter was a sub-sample of the
national Malaria Indicator Survey (MIS 3R). Each survey wave used multi-stage cluster random
sampling with 25 households per cluster (224 clusters with 5,730 households in Baseline 2006
and 245 clusters with 5,910 households in MIS 3R 2007). Net ownership was assessed by visual
inspection while net utilization was reported as use of the net the previous night. This net level
analysis was restricted to households owning at least one net of any type. Logistic regression
models of association between net use and explanatory variables including net type, age,
condition, cost and other household characteristics were undertaken using generalized linear
latent and mixed models (GLLAMM). RESULTS: A total of 3,784 nets in 2,430 households were
included in the baseline 2006 analysis while the MIS 3R 2007 analysis comprised 5,413 nets in
3,328 households. The proportion of nets used the previous night decreased from 85.1% to
56.0% between baseline 2006 and MIS 3R 2007, respectively. Factors independently associated
with increased proportion of nets used were: LLIN net type (at baseline 2006); indoor residual
spraying (at MIS 3R 2007); and increasing wealth index at both surveys. At both baseline 2006
Updated March 9, 16
and MIS 3R 2007, reduced proportion of nets used was independently associated with
increasing net age, increasing damage of nets, increasing household net density, and increasing
altitude (>2,000m). CONCLUSION: This study identified modifiable factors affecting use of nets
that were consistent across both surveys. While net replacement remains important, the
findings suggest that: more education about use and care of nets; making nets more resistant
to damage; and encouraging net mending are likely to maximize the huge investment in scale
up of net ownership by ensuring they are used. Without this step, the widespread benefits of
LLIN cannot be realized.
Ngondi JM, Graves PM, Gebre T, Mosher AW, Shargie EB, Emerson PM, Richards FO, Ethiopia
EM. Which nets are being used: factors associated with mosquito net use in Amhara, Oromia
and Southern Nations, Nationalities and Peoples' Regions of Ethiopia. Malar J 2011, 10:92.
1.6 How much does malaria vector control quality matter: the epidemiological
impact of holed nets and inadequate indoor residual spraying.
Background: Insecticide treated nets (ITN) and indoor residual spraying (IRS) are the two pillars
of malaria vector control in Africa, but both interventions are beset by quality and coverage
concerns. Data from three control programs were used to investigate the impact of: 1) the
physical deterioration of ITNs, and 2) inadequate IRS spray coverage, on their respective
protective effectiveness. Methods: Malaria indicator surveys were carried out in 2009 and 2010
in Bioko Island, mainland Equatorial Guinea and Malawi to monitor infection with P.falciparum
in children, mosquito net use, net condition and spray status of houses. Nets were classified by
their condition. The association between infection and quality and coverage of interventions
was investigated. Results: There was reduced odds of infection with P.falciparum in children
sleeping under ITNs that were intact (Odds ratio (OR): 0.65, 95% CI: 0.55-0.77 and OR: 0.81,
95% CI: 0.56-1.18 in Equatorial Guinea and in Malawi respectively), but the protective effect
became less with increasingly worse condition of the net. There was evidence for a linear trend
in infection per category increase in deterioration of nets. In Equatorial Guinea IRS offered
protection to those in sprayed and unsprayed houses alike when neighbourhood spray
coverage was high ($80%) compared to those living in areas of low IRS coverage (,20%),
regardless of whether the house they lived in was sprayed or not (adjusted OR = 0.54, 95% CI
0.33-0.89). ITNs provided only personal protection, offering no protection to non users.
Although similar effects were seen in Malawi, the evidence was much weaker than in Equatorial
Guinea. Conclusions: Universal coverage strategies should consider policies for repair and
replacement of holed nets and promote the care of nets by their owners. IRS programs should
ensure high spray coverage since inadequate coverage gives little or no protection at all.
Rehman AM, Coleman M, Schwabe C, Baltazar G, Matias A, Gomes IR, Yellott L, Aragon C,
Nchama GN, Mzilahowa T, Rowland M, Kleinschmidt I. How much does malaria vector control
quality matter: the epidemiological impact of holed nets and inadequate indoor residual
spraying. PLoS One 2011, 6:e19205.
Updated March 9, 16
1.7 Factors associated with mosquito net use by individuals in households owning
nets in Ethiopia.
BACKGROUND: Ownership of insecticidal mosquito nets has dramatically increased in Ethiopia
since 2006, but the proportion of persons with access to such nets who use them has declined.
It is important to understand individual level net use factors in the context of the home to
modify programmes so as to maximize net use. METHODS: Generalized linear latent and mixed
models (GLLAMM) were used to investigate net use using individual level data from people
living in net owning households from two surveys in Ethiopia: baseline 2006 included 12,678
individuals from 2,468 households and a sub-sample of the Malaria Indicator Survey (MIS) in
2007 included 14,663 individuals from 3,353 households. Individual factors (age, sex,
pregnancy); net factors (condition, age, net density); household factors (number of rooms
[2006] or sleeping spaces [2007], IRS, women's knowledge and school attendance [2007 only],
wealth, altitude); and cluster level factors (rural or urban) were investigated in univariate and
multi-variable models for each survey. RESULTS: In 2006, increased net use was associated
with: age 25-49 years (adjusted (a) OR = 1.4, 95% confidence interval (CI) 1.2-1.7) compared to
children U5; female gender (aOR = 1.4; 95% CI 1.2-1.5); fewer nets with holes (Ptrend = 0.002);
and increasing net density (Ptrend < 0.001). Reduced net use was associated with: age 5-24
years (aOR = 0.2; 95% CI 0.2-0.3). In 2007, increased net use was associated with: female
gender (aOR = 1.3; 95% CI 1.1-1.6); fewer nets with holes (aOR [all nets in HH good] = 1.6; 95%
CI 1.2-2.1); increasing net density (Ptrend < 0.001); increased women's malaria knowledge
(Ptrend < 0.001); and urban clusters (aOR = 2.5; 95% CI 1.5-4.1). Reduced net use was
associated with: age 5-24 years (aOR = 0.3; 95% CI 0.2-0.4); number of sleeping spaces (aOR
[per additional space] =0.6, 95% CI 0.5-0.7); more old nets (aOR [all nets in HH older than 12
months] = 0.5; 95% CI 0.3-0.7); and increasing household altitude (Ptrend < 0.001).
CONCLUSION: In both surveys, net use was more likely by women, if nets had fewer holes and
were at higher net per person density within households. School-age children and young adults
were much less likely to use a net. Increasing availability of nets within households (i.e.
increasing net density), and improving net condition while focusing on education and
promotion of net use, especially in school-age children and young adults in rural areas, are
crucial areas for intervention to ensure maximum net use and consequent reduction of malaria
transmission.
Graves PM, Ngondi JM, Hwang J, Getachew A, Gebre T, Mosher AW, Patterson AE, Shargie EB,
Tadesse Z, Wolkon A, Reithinger R, Emerson PM, Richards FO. Factors associated with
mosquito net use by individuals in households owning nets in Ethiopia. Malar J 2011, 10:354.
1.8 Mosquito nets in a rural area of Western Kenya: ownership, use and quality.
Background Insecticide-treated nets (ITNs) are regarded as one of the most effective strategies
to prevent malaria in Africa. This study analyses the use and quality of nets owned by
households in an area of high net coverage. Methods A structured questionnaire on ownership
and use of nets was administered to the households of individuals sampled from a local health
centre in south Kisii district, Kenya. A physical inspection of all the nets in the households was
Updated March 9, 16
done and their conditions recorded on spot check forms designed for that purpose. Results Of
the 670 households surveyed, 95% owned at least one net. Only 59% of household residents
slept under a net during the night prior to the survey. 77% of those who slept under a net used
an insecticide-treated net (ITN) or long-lasting insecticide-treated nets (LLIN). Out of 1,627 nets
in the survey households, 40% were deemed to be of poor quality because of holes. Compared
to other age groups, children aged 5-14 years were most likely to have slept under nets of poor
quality (odds ratio 1.41; p= 0.007). Conclusions Although net ownership was high following
increased delivery of ITNs, continuous promotion of effective maintenance and routine use is
needed and efforts to replace damaged nets must be implemented.
Githinji S, Herbst S, Kistemann T, Noor AM. Mosquito nets in a rural area of Western Kenya:
ownership, use and quality. Malar J 2010, 9:250.
1.9 Determining and addressing obstacles to the effective use of long-lasting
insecticide-impregnated nets in rural Tanzania
BACKGROUND: The objective of this project was to achieve high, sustainable levels of net
coverage in a village in rural Tanzania by combining free distribution of long-lasting insecticideimpregnated nets (LLINs) with community-tailored education. In Tanzania, malaria is the
leading cause of morbidity and mortality. Although malaria bed nets have a well-established
role in reducing disease burden, few rural households have access to nets, and effective use
depends on personal practices and attitudes. METHODS: Five practices and attitudes
inconsistent with effective LLIN use were identified from household interviews (n = 10). A
randomized survey of villagers (n = 132) verified local prevalence of these practices and
attitudes. Community leaders held an educational session for two members of every household
addressing these practice and attitudes, demonstrating proper LLIN use, and emphasizing
behaviour modification. Attendees received one or two LLINs per household. Surveys
distributed three weeks (n = 104) and 15 months (n = 104) post-intervention assessed corrected
practices and attitudes. Project efficacy was defined by correction of baseline practices and
attitudes as well as high rates of reported daily net use, with statistical significance determined
by chi-square test. RESULTS: Baseline interviews and surveys revealed incorrect practices and
attitudes regarding 1) use of nets in dry season, 2) need to retreat LLINs, 3) children napping
under nets, 4) need to repair nets, and 5) net procurement as a priority, with 53- 88.6%
incorrect responses (11.4-47% correct responses). A three-week follow-up demonstrated 8395% correct responses. Fifteen-month follow-up showed statistically significant (p < 0.01)
corrections from baseline in all five practice and attitudes (39.4-93.3% correct answers). 89.4%
of respondents reported using their nets every night, and 93.3% affirmed purchase of nets as a
financial priority. CONCLUSIONS: Results suggest that addressing community-specific practices
and attitudes prior to LLIN distribution promotes consistent and correct use, and helps change
attitudes towards bed nets as a preventative health measure. Future LLIN distributions can
learn from the paradigm established in this project.
Updated March 9, 16
Widmar M, Nagel CJ, Ho DY, Benziger PW, Hennig N. Determining and addressing obstacles to
the effective use of long-lasting insecticide-impregnated nets in rural Tanzania. Malar J 2009,
8:315.
1.10 Culturally compelling strategies for behaviour change: a social ecology model
and case study in malaria prevention.
Behaviour change is notoriously difficult to initiate and sustain, and the reasons why efforts to
promote healthy behaviours fail are coming under increasing scrutiny. To be successful, health
interventions should build on existing practices, skills and priorities, recognise the constraints
on human behaviour, and either feature community mobilisation or target those most
receptive to change. Furthermore, interventions should strive to be culturally compelling, not
merely culturally appropriate: they must engage local communities and nestle within social and
ecological landscapes. In this paper, we propose a social ecology perspective to make explicit
the links between intention to change, actual behaviour change, and subsequent health impact,
as relating to both theory-based models and practical strategies for triggering behaviour
change. A social ecology model focuses attention on the contexts of behaviour when designing,
implementing or critically evaluating interventions. As a case study, we reflect on a communitydirected intervention in rural Gambia designed to reduce malaria by promoting a relatively
simple and low-cost behaviour: repairing holes in mosquito bednets. In phase 1, contextual
information on bednet usage, transactions and repairs (the 'social lives' of nets) was
documented. In phase 2 (intervention), songs were composed and posters displayed by
community members to encourage repairs, creating a sense of ownership and a compelling
medium for the transmission of health messages. In phase 3 (evaluation), qualitative and
quantitative data showed that household responses were particularly rapid and extensive, with
significant increase in bednet repairs (p<0.001), despite considerable constraints on human
agency. We highlight a promising approach-using songs-as a vehicle for change, and present a
framework to embed the design, implementation and critical evaluation of interventions within
the larger context-or social ecology-of behaviour practices that are the bedrock of health
interventions.
Panter-Brick C, Clarke SE, Lomas H, Pinder M, Lindsay SW. Culturally compelling strategies for
behaviour change: a social ecology model and case study in malaria prevention. Soc Sci Med
2006, 62:2810-25.
1.11 Maintenance behaviour and long-lasting insecticide-treated nets (LLITNs)
previously introduced into Bourapar district, Khammouane province, Lao PDR.
BACKGROUND: Long-lasting insecticide-treated nets (LLITNs) are expected to be an important
advance in malaria control, but operational experience is still scarce. This study presents some
operational findings concerning the introduction of Olyset LLITNs (Sumitomo Chemical Co., Ltd,
Japan) in Laos. The study site, Bourapar district, a remote district at high risk of malaria,
Updated March 9, 16
received Olyset nets during 1999-2000. After distribution of the nets the number of malaria
cases in the district hospital decreased for a time, however it began to rise again a year after
the intervention. To sustain the effect of the nets, net users were given instructions on
maintenance and use. This study aimed to investigate the condition of Olyset nets and the
maintenance behaviour of net users after 2-3 years of use, and to examine the associations
between maintenance behaviour and the number of malaria episodes during the previous year.
METHODS: Questionnaire interviews and inspections of nets were conducted at 240
households during February-March 2003. RESULTS: About 40% of the observed nets had
holes/were torn, and the maintenance instructions had not been followed sufficiently.
Households following the recommended washing frequency (38.2%) reported fewer malaria
episodes during the past year, which demonstrates the importance of the recommended
washing frequency in the effective use of the nets. CONCLUSIONS: Our study promotes the idea
that, in addition to pursuing high coverage of LLITNs, more effort should be made to ensure
that nets are kept in good condition in future LLITN programmes.
Shirayama Y, Phompida S, Kuroiwa C, Miyoshi M, Okumura J, Kobayashi J. Maintenance
behaviour and long-lasting insecticide-treated nets (LLITNs) previously introduced into
Bourapar district, Khammouane province, Lao PDR. Public Health 2007, 121:122-9.
1.12 Field issues related to effectiveness of insecticide-treated nets in Tanzania.
Insecticide-treated nets (ITNs) impregnated with pyrethroid insecticides have become one of
the most promising interventions to prevent malaria in highly endemic areas. Despite the large
body of experience documenting their health impact and the best way to distribute them, some
key practical issues remain unresolved. For example, the duration of effective life of a net under
field conditions is unknown. The most important factor affecting net effectiveness is the issue
of regular re-treatment with insecticide. Washing is also an important determinant of
insecticide longevity in the field. Trials were undertaken to provide some essential field
information on ITNs within the site of an extended ITN programme in the Morogoro region of
Tanzania. It was found that 45% of all nets were in bad condition (defined as more than seven
large holes). It is concluded that an effective 'life' for polyester nets is 2-3 years. Further, twothirds of the 20% of nets that were reported as having been re-treated within the last 12
months had less than 5 mg/m(2) of insecticide. According to the World Health Organization this
is insufficient to be effective. People reported that they washed their nets four to seven times
per year, usually with soap. Observations showed that such washing does not harm the nets
and that the wash-water was unlikely to have an impact on the environment. Finally, bioassays
were carried out with Anopheles gambiae on polyester netting with 0.5, 2, 5, 10 and 30
mg/m(2) of deltamethrin, alphacypermethrin and lambdacyhalothrin to assess the
effectiveness of pyrethroids. The results confirmed that even with low insecticide
concentrations, nets can still provide partial protection.
Erlanger TE, Enayati AA, Hemingway J, Mshinda H, Tami A, Lengeler C. Field issues related to
effectiveness of insecticide-treated nets in Tanzania. Med Vet Entomol 2004, 18:153-60.
Updated March 9, 16
2 Evaluation of Nets After a Period of Time
2.1 Evidence for a useful life of more than three years for a polyester-based longlasting insecticidal mosquito net in Western Uganda.
BACKGROUND: Long-lasting insecticidal nets (LLIN) are now standard for the prevention of
malaria. However, only products with recommendation for public use from the World Health
Organization should be used and this evaluation includes the assessment of net effectiveness
after three years of field use. Results for one of the polyester-based products, Interceptor(R) is
presented. METHODS: In five villages, 190 LLIN and 90 nets conventionally treated with the
insecticide alpha-cypermethrin at 25 mg/m^2 were distributed randomly and used by the
families. Following a baseline household survey a net survey was carried out every six months
to capture use, washing habits and physical condition of the nets. Randomly selected nets were
collected after 6, 12, 24, 36 and 42 months and tested for remaining insecticide content and
ability to knock-down and kill malaria transmitting mosquitoes. RESULTS: During the three and
a half years of observation only 16 nets were lost to follow-up resulting in an estimated
attrition rate of 12% after three and 20/% after 3.5 years. Nets were used regularly and washed
on average 1.5 times per year. After three and a half years 29% of the nets were still in good
condition while 13% were seriously torn with no difference between the LLIN and control nets.
The conventionally treated nets quickly lost insecticide and after 24 months only 7% of the
original dose remained (1.6 mg/m^2). Baseline median concentration of alpha-cypermethrin for
LLIN was 194.5 mg/m^2 or 97% of the target dose with between and within net variation of
11% and 4 % respectively (relative standard deviation). On the LLIN 73.8 mg/m^2 alphacypermethrin remained after three years of use and 56.2 mg/m^2 after three and a half and
94% and 81% of the LLIN still had >15 mg/m^2 left respectively. Optimal effectiveness in bioassays ([greater than or equal to]95% 60 minute knock-down or [greater than or equal to] 80%
24 hour mortality) was found in 83% of the sampled LLIN after three and 71% after three and a
half years. CONCLUSIONS: Under conditions in Western Uganda the tested long-lasting
insecticidal net Interceptor(R) fulfilled the criteria for phase III of WHO evaluations and, based
on preliminary criteria of the useful life, this product is estimated to last on average between
three and four years.
Kilian A, Byamukama W, Pigeon O, Gimnig J, Atieli F, Koekemoer LL, Protopopoff N. Evidence
for a useful life of more than three years for a polyester-based long-lasting insecticidal
mosquito net in Western Uganda. Malar J 2011, 10:299.
2.2 Evaluation of Interceptor long-lasting insecticidal nets in eight communities in
Liberia.
BACKGROUND: By 2008, the WHO Pesticide Evaluation Scheme (WHOPES) recommended five
long-lasting insecticidal nets (LLINs) for the prevention of malaria: Olyset((R)), PermaNet
2.0((R)), Netprotect((R)), Duranet((R)) and Interceptor((R)). Field information is available for
both Olyset(R) and PermaNet((R)), with limited data on the newer LLINs. To address this gap, a
field evaluation was carried out to determine the acceptability and durability of Interceptor((R))
LLINs. METHODS: A one-year prospective field study was conducted in eight rural returnee
Updated March 9, 16
villages in Liberia. Households were randomized to receive Interceptor((R)) LLINs or
conventionally treated nets (CTNs). Primary outcomes were levels of residual alphacypermethrin measured by HPLC and participant utilization/acceptability of the ITNs. RESULTS:
A total of 398 nets were analysed for residual alpha-cypermethrin. The median baseline
concentrations of insecticide were 175.5 mg/m2 for the Interceptor((R)) LLIN and 21.8 mg/m2
for the CTN. Chemical residue loss after a one year follow-up period was 22% and 93%
respectively. Retention and utilization of nets remained high (94%) after one year, irrespective
of type, while parasitaemia prevalence decreased from 29.7% at baseline to 13.6% during the
follow up survey (p = < 0.001). Interview and survey data show perceived effectiveness of ITNs
was just as important as other physical attributes in influencing net utilization. CONCLUSION:
Interceptor((R)) LLINs are effective and desirable in rural communities in Liberia. Consideration
for end user preferences should be incorporated into product development of all LLINs in the
future, in order to achieve optimum retention and utilization.
Banek K, Kilian A, Allan R. Evaluation of Interceptor long-lasting insecticidal nets in eight
communities in Liberia. Malar J 2010, 9:84.
2.3 Loss of protection with insecticide-treated nets against pyrethroid-resistant
Culex quinquefasciatus mosquitoes once nets become holed: an experimental
hut study.
BACKGROUND: An important advantage of pyrethroid-treated nets over untreated nets is that
once nets become worn or holed a pyrethroid treatment will normally restore protection. The
capacity of pyrethroids to kill or irritate any mosquito that comes into contact with the net and
prevent penetration of holes or feeding through the sides are the main reasons why treated
nets continue to provide protection despite their condition deteriorating over time. Pyrethroid
resistance is a growing problem among Anopheline and Culicine mosquitoes in many parts of
Africa. When mosquitoes become resistant the capacity of treated nets to provide protection
might be diminished, particularly when holed. An experimental hut trial against pyrethroidresistant Culex quinquefasciatus was therefore undertaken in southern Benin using a series of
intact and holed nets, both untreated and treated, to assess any loss of protection as nets
deteriorate with use and time. RESULTS: There was loss of protection when untreated nets
became holed; the proportion of mosquitoes blood feeding increased from 36.2% when nets
were intact to between 59.7% and 68.5% when nets were holed to differing extents. The
proportion of mosquitos’ blood feeding when treated nets were intact was 29.4% which
increased to 43.6-57.4% when nets were holed. The greater the number of holes the greater
the loss of protection regardless of whether nets were untreated or treated. Mosquito
mortality in huts with untreated nets was 12.9-13.6%; treatment induced mortality was less
than 12%. The exiting rate of mosquitoes into the verandas was higher in huts with intact nets.
CONCLUSION: As nets deteriorate with use and become increasingly holed the capacity of
pyrethroid treatments to restore protection is greatly diminished against resistant Culex
quinquefasciatus mosquitoes.
Updated March 9, 16
Irish S, N'guessan R, Boko P, Metonnou C, Odjo A, Akogbeto M, Rowland M. Loss of protection
with insecticide-treated nets against pyrethroid-resistant Culex quinquefasciatus mosquitoes
once nets become holed: an experimental hut study. Parasit Vectors 2008, 1:17.
2.4 An experimental hut evaluation of Olyset® nets against anopheline mosquitoes
after seven years use in Tanzanian villages
BACKGROUND: Long-lasting insecticidal nets (LLINs) are advocated by WHO for protection
against malaria. Of the three brands of LLINs currently approved by WHO, Olyset(R) is the only
one currently granted full recommendation. With this type of LLIN, the insecticide (permethrin)
is incorporated into the polyethylene fibre during manufacture and diffuses from the core to
the surface, thereby maintaining surface concentrations. It has not been determined for how
long Olyset nets remain protective against mosquitoes in household use. METHODS: Examples
of Olyset nets, which had been in use in Tanzanian villages for seven years, were tested in
experimental huts against naturally entering Anopheles gambiae and Anopheles funestus
mosquitoes. Performance was compared with new Olyset nets, conventionally treated ITNs
(either newly treated with alphacypermethrin or taken from local villages after 1.5 years of use)
and untreated nets. All nets were artificially holed except for the seven-year Olyset nets, which
had developed holes during prolonged domestic use. RESULTS: Anopheles funestus and An.
gambiae in NE Tanzania are susceptible to pyrethroids. The new Olyset nets caused high
mortality against An. funestus (73.9%) and An. gambiae (62.7%) in experimental huts. The
seven-year Olyset nets caused 58.9% mortality against An. funestus and 40.0% mortality against
An. gambiae. The freshly treated alphacypermethrin nets also caused high mortality against An.
funestus (70.6%) and An. gambiae (72.0%); this decreased to 58.4% and 69.6% respectively
after 1.5 years of use. The new Olyset nets inhibited blood-feeding by 40-50%. The 7 year
Olyset nets showed no feeding inhibition over that shown by the untreated nets. The
alphacypermethrin treated nets failed to inhibit blood-feeding after 1.5 years of use. However
iHhhdn laboratory tunnel tests samples of all types of treated net including the 7 year Olyset
inhibited blood-feeding by more than 95%. CONCLUSION: After seven years of use Olyset nets
were still strongly insecticidal. Mosquito mortality decreased by only 20-35% over this period.
However, Olyset would not provide personal protection after seven years unless it was in good
condition and all holes fully repaired.
Malima RC, Magesa SM, Tungu PK, Mwingira V, Magogo FS, Sudi W, Mosha FW, Curtis CF,
Maxwell C, Rowland M. An experimental hut evaluation of Olyset nets against anopheline
mosquitoes after seven years use in Tanzanian villages. Malar J 2008, 7:38.
2.5 Evaluation of long-lasting insecticidal nets after 2 years of household use.
Development of long-lasting insecticidal nets (LLINs) may eliminate the need for insecticide
retreatment of ITNs. While two LLINs (Olyset, Sumitomo Chemical Co., Japan; and PermaNet
1.0, Vestergaard-Frandsen, Denmark) have received recommendations from the World Health
Organization Pesticide Evaluation Scheme, field-testing under normal use has been limited. We
used a survival analysis approach to compare time to net failure of conventional polyester
Updated March 9, 16
bednets treated only with deltamethrin to two LLINs and two candidate LLINs (Olyset;
PermaNet; Insector, Athanor, France; and Dawa, Siamdutch Mosquito Netting Co., Thailand).
Additionally, we evaluated nets treated with a process designed to increase the wash-durability
of permethrin-treated nets through the addition of cyclodextrin (a starch) in the treatment
process. Houses in western Kenya were randomly assigned to one of the six net types and nets
were distributed to cover all sleeping spaces. Households were visited monthly to assess
reported side effects in inhabitants and washing frequency. Nets were evaluated for insecticidal
activity by periodic WHO cone bioassays with mortality assessed at 24 h. Nets with bioassay
mortality <70% were assayed monthly until failure, defined as the first of two consecutive
bioassay mortality rates <50%. Time to failure was analyzed using an extended Cox Proportional
Hazards model controlling for the cumulative number of washes. We distributed 314 nets to
177 households in June-July 2002; 22 nets (7.0%) were lost to follow-up and 196 (62.4%) failed
during the first 2 years of the evaluation. Controlling for cumulative number of washes,
PermaNet 1.0 [Hazard Ratio (HR) 0.14, 95% Confidence Interval (CI) 0.06-0.31] had a
significantly lower risk of failure than conventional nets while Insector had a significantly higher
risk of failure (HR 2.57, 95% CI 1.06-4.15). The risks of failure of the remaining nets (Olyset: HR
1.29, 95% CI 0.79-2.10; Dawa: HR 0.58, 95% CI 0.32-1.18; cyclodextrin: HR 0.65, 95% CI 0.40-1.1)
were not significantly different from that of a conventional net. PermaNet 1.0 performed
significantly better than conventional nets and should be recommended to malaria control
programs.
Lindblade KA, Dotson E, Hawley WA, Bayoh N, Williamson J, Mount D, Olang G, Vulule J,
Slutsker L, Gimnig J. Evaluation of long-lasting insecticidal nets after 2 years of household use.
Trop Med Int Health 2005, 10:1141-50.
2.6 Evaluation of Olyset insecticide-treated nets distributed seven years previously
in Tanzania.
BACKGROUND: Insecticide-treated nets represent currently a key malaria control strategy, but
low insecticide re-treatment rates remain problematic. Olyset nets are currently one of two
long-lasting insecticidal nets recommended by WHO. An assessment was carried out of the
effect of Olyset nets after seven years of use in rural Tanzania. METHODS: A survey of Olyset
nets was conducted in two Tanzanian villages to examine their insecticide dosage, bioassay
efficacy and desirability compared with ordinary polyester nets. RESULTS: Of 103 randomly
selected nets distributed in 1994 to 1995, 100 could be traced. Most nets were in a condition
likely to offer protection against mosquito biting. Villagers appreciated mainly the durability of
Olyset trade mark nets and insecticide persistence. People disliked the small size of these nets
and the light blue colour and preferred a smaller mesh size, features that can easily be
modified. At equal price, 51% said they would prefer to buy an Olyset net and 49% opted for an
ordinary polyester net. The average permethrin content was 33%-41% of the initial insecticide
dose of 20,000 mg/Kg. Bioassay results indicated high knock-down rates at 60 minutes, but the
mosquito mortality after 24 hours was rather low (mean: 34%). No significant correlation was
found between bioassay results and insecticide concentration in and on the net. CONCLUSIONS:
Olyset nets are popular, durable and with a much longer insecticide persistence than ordinary
Updated March 9, 16
polyester nets. Hence, Olyset nets are one of the best choices for ITN programmes in rural
malaria-endemic areas.
Tami A, Mubyazi G, Talbert A, Mshinda H, Duchon S, Lengeler C. Evaluation of Olyset
insecticide-treated nets distributed seven years previously in Tanzania. Malar J 2004, 3:19.
3 Wash Resistance
3.1 Wash resistance and efficacy of three long-lasting insecticidal nets assessed from
bioassays on Anopheles culicifacies and Anopheles stephensi.
OBJECTIVE: To test the wash resistance and efficacy of long-lasting insecticidal nets (LLINs),
namely Olyset Net and PermaNet 2.0; and a long-lasting treatment kit, K-O Tab 1-2-3, on
Anopheles culicifacies and An. stephensi, major malaria vectors in India, by bioassays.
Conventionally treated deltamethrin net (CTDN with K-O Tab) was used for comparison.
METHOD: Mortality and median time for knockdown (MTKD) of mosquitoes were determined
using contact bioassays and ball frame bioassays respectively. Hand washing and machine
washing were used. RESULTS: LLINs showed good bio-efficacy against An. culicifacies and An.
stephensi. The mortality of mosquitoes remained >80% after up to 20 hand washes and up to
15 machine washes on all LLINs tested. No significant differences were observed in mortalities
between the An. culicifacies and An. stephensi in cone bioassays (P > 0.05). MTKD increased
progressively with successive washes and there was a significant difference in median time for
knockdown of test mosquitoes and between hand-washed and machine-washed nets (P < 0.05).
Sreehari U, Raghavendra K, Rizvi MM, Dash AP. Wash resistance and efficacy of three longlasting insecticidal nets assessed from bioassays on Anopheles culicifacies and Anopheles
stephensi. Trop Med Int Health 2009, 14:597-602.
3.2 Evaluation of the wash resistance of three types of manufactured insecticidal
nets in comparison to conventionally treated nets.
The present study evaluated the efficacy and wash resistance of several commercial
deltamethrin-treated nets (PermaNet, from factory (PN-F) and market (PN-M), Yorkool (Y) and
AZ net) that were claimed by the manufacturers to be Long-Lasting Insecticide Treated Nets
(LLITNs), compared to ITNs conventionally treated with deltamethrin (23-27 mg/m(2), using one
K-O Tab tablet (KO) per net). Montpellier washing technique was used for washing the pieces of
the nets. Insecticidal activity was assessed on dried pieces of nets after 0, 2, 5, 8, 11, 15, 18 and
21 washes, using two types of bioassay (mean median knock down times and mortality 24 h
after a 3-min exposure) and reared female Anopheles stephensi. To evaluate the effect of heat
on diffusion of insecticide from inside of the nets to the surface of them, some Permanet nets
were heated. For all the types of nets tested the median knock down time (MKDT) increased
Updated March 9, 16
approximately linearly with number of washes. The slopes of the lines (increase of MKDT per
wash) were low with the PN-F and PN-M, intermediate with Y and equally high with KO and AZ.
No significant differences can be claimed with the 3-min exposure tests. The slopes of the
regression lines did not differ significantly between the heated and unheated samples. It is
concluded that diffusion at ambient temperature is fast enough to rapidly compensate for the
loss of insecticide on the surface with no need to artificially stimulate diffusion by heating.
Kayedi MH, Lines JD, Haghdoost AA. Evaluation of the wash resistance of three types of
manufactured insecticidal nets in comparison to conventionally treated nets. Acta Trop 2009,
111:192-6.
3.3 Wash resistance of PermaNets in comparison to hand-treated nets.
The wash resistance of factory produced PermaNets (with deltamethrin bonded to the netting
with a resin) was studied by bioassays with Anopheles stephensi. Commercial detergent
powders were used to wash the nets. For comparison, conventionally treated nets were
washed and bio-assayed. Nets were washed under laboratory conditions using a Rotary shaker
for 10min. Mosquito bioassays used standard WHO plastic cones with an exposure time of
3min. The PermaNet caused almost a 100% mortality of An. stephensi after up to 18 washes
and >80% mortality up to 26 washes but after 30 washes mortality declined. The differences
between the mortality of An. stephensi on treated nets washed with detergent or soap
(uncoloured, non-perfumed) were not significant. When conventional nets dipped in
deltamethrin (25mg/m(2)) or lambdacyhalothrin (10mg/m(2)) were washed under similar
laboratory conditions, the wash resistance was markedly less than that of the PermaNet. In the
case of deltamethrin, mosquito mortality remained >80% up to 12 washes and with
lambdacyhalothrin mortality remained above 80% up to 11 washes. The relationship of 80%
mortality from a 3min bioassay to effectiveness against free flying mosquitoes remains to be
determined.
Gunasekaran K, Vaidyanathan K. Wash resistance of PermaNets in comparison to hand-treated
nets. Acta Trop 2008, 105:154-7.
3.4 Evaluation of the effects of repeated hand washing, sunlight, smoke and dirt on
the persistence of deltamethrin on insecticide-treated nets.
Field studies were carried out in Iran to evaluate the effect of various factors (washing, sun,
smoke, dust and dirt) on the residual insecticidal activity of PermaNet (a brand of long-lasting
insecticidal net), and on nets conventionally treated with deltamethrin (K-O Tab), using
bioassay tests. Thirty-two nets were washed five or 15 times, and eight nets were not washed
at all. Nets were washed vigorously in cold tap water (17 degrees C, pH 8.9) with a detergent.
Hand rubbing continued for 3min. After washing, some nets were exposed to dense smoke
from a dung-hay fire for 3min and were also left exposed to the dusty wind between washes.
One group of nets was exposed to the sunlight for the full 3-d interval between washes;
another was exposed to sunlight for just 3h after each wash; two other groups were kept in the
Updated March 9, 16
shade. There was a significantly greater loss of activity in nets exposed to the sun throughout
the 3-d interval between washes: that is, for a total of 15 to 45 d. However, short sunlight
exposure (maximum 3h between washes) during drying did not have any effect. We did not find
any significant effect of exposure to dirt, dust and smoke after washing. It is concluded that the
effect of sun is much smaller than that of washing, and that drying nets for a few hours in the
sun is not harmful.
Kayedi MH, Lines JD, Haghdoost AA, Vatandoost MH, Rassi Y, Khamisabady K. Evaluation of the
effects of repeated hand washing, sunlight, smoke and dirt on the persistence of deltamethrin
on insecticide-treated nets. Trans R Soc Trop Med Hyg 2008, 102:811-6.
3.5 A randomized and controlled comparison of the wash-resistances and
insecticidal efficacies of four types of deltamethrin-treated nets, over a 6-month
period of domestic use with washing every 2 weeks, in a rural area of Iran.
In a randomized, prospective, 6-month-long field study in a rural area of Iran, the wash
resistances of 200 nets (40 PermaNet, 40 Yorkool and 40 A-Z nets), that their manufacturers
claimed be long-lasting insecticidal nets (LLIN), were compared with those of 40 nets
conventionally treated with deltamethrin (using K-O Tab tablets). All the nets were kept in
routine domestic use and subjected to standardized hand-washing at 2-week intervals. Wildcaught or laboratory-reared Anopheles stephensi were used for the bio-assays of insecticidal
activity. The regular washing and domestic use led to reductions in the insecticidal activities of
all the treated nets after 6 months. Although the PermaNet nets showed the smallest
reduction, they were not significantly better than the conventionally treated nets, which still
showed acceptable insecticidal activity after 6 months. The PermaNet and A-Z nets both
performed significantly better than the Yorkool nets, which were slightly but not significantly
worse than the conventionally treated nets. In questionnaire-based interviews, the local
householders were found to wash their own (non-study) nets at median and mean frequencies
of every 2 and 2.1 weeks, respectively. In conclusion, the PermaNet nets showed better wash
resistance than any of the other commercial nets, and were the only commercial nets tested
that truly appeared to be LLIN. There still appears to be scope, however, for the impregnation,
and thus the wash-resistance, of even the PermaNet nets to be improved.
Kayedi MH, Lines JD, Haghdoost AA, Najafi S. A randomized and controlled comparison of the
wash-resistances and insecticidal efficacies of four types of deltamethrin-treated nets, over a 6month period of domestic use with washing every 2 weeks, in a rural area of Iran. Ann Trop
Med Parasitol 2007, 101:519-28.
3.6 Multi-country field trials comparing wash-resistance of PermaNet and
conventional insecticide-treated nets against anopheline and culicine
mosquitoes.
Insecticide-treated bednets (ITNs) are commonly used as a means of personal protection from
malaria transmission by anopheline mosquitoes (Diptera: Culicidae). Long-lasting insecticidal
Updated March 9, 16
nets (LLINs) have special treatments intended to remain effective after many washes. The
present trials assessed the efficacy and wash-resistance of several production batches of
PermaNet (polyester net coated with polymer resin containing pyrethroid insecticide
deltamethrin 55 mg ai/m2) against malaria vectors in Pakistan, Iran and Tanzania compared to
ITNs conventionally treated with alphacypermethrin 15 or 20 mg ai/m2, or deltamethrin 25 or
50 mg ai/m2. Insecticidal efficacy of the nets before and after repeated washing (using W.H.O.
recommended and traditional local washing procedures) was monitored through contact
bioassays with Anopheles and by experimental hut and outdoor platform tests. Local washing
regimes gradually reduced the insecticidal efficacy of conventionally treated nets, but they
were not exhausted, even after 21 washes. Using a more rigorous laboratory washing method,
insecticide was more readily stripped from conventionally treated nets. PermaNet retained high
efficacy after 21 washes, giving more than 97% mortality of Anopheles in contact bioassays with
3-min exposure. Using the more sensitive bioassay criterion of 'median time to knockdown',
PermaNet showed no loss of insecticidal activity against Anopheles after washing repeatedly in
2 out of 6 trials; whereas in a further three trials knockdown activity of PermaNet and
conventional ITNs declined at comparable rates. Higher mortality levels of Anopheles in contact
bioassays did not always translate to superiority in experimental hut or enclosed platform trials.
In only one of four comparative field trials did PermaNet out-perform conventional ITNs after
washing: this was in the trial of PermaNet 2.0--the product with improved quality assurance.
Because PermaNet and conventionally treated nets were both quite tolerant of local washing
procedures, it is important in field trials to compare LLINs with conventional ITNs washed an
equivalent number of times. Our comparison of PermaNet 2.0 against conventionally treated
deltamethrin nets (CTDN) in Pakistan demonstrated superior performance of the LLIN after 20
washes in phase I and phase II bioassays, and this was corroborated by chemical assays of
residual deltamethrin. Although PermaNet 2.0 has received WHOPES interim recommendation
for malaria control purposes, its performance should be monitored in everyday use throughout
its lifespan in various cultural settings to assess its durability and long-term effectiveness for
malaria prevention and control. As many millions of conventionally treated nets are already in
routine use, and these will require regular re-treatment, programme strategies should be
careful to preserve the effectiveness of ITNS before and after establishing the reliability of LLINs
in long-term use.
Graham K, Kayedi MH, Maxwell C, Kaur H, Rehman H, Malima R, Curtis CF, Lines JD, Rowland
MW. Multi-country field trials comparing wash-resistance of PermaNet and conventional
insecticide-treated nets against anopheline and culicine mosquitoes. Med Vet Entomol 2005,
19:72-83.
3.7 Laboratory wash resistance of long-lasting insecticidal nets.
Long-lasting insecticidal nets (LLINs) may eliminate the need for retreatment of mosquito nets
used for the control of malaria and other vector-borne diseases. The efficacy of LLINs after
repeated washing under laboratory conditions has been used to predict long-lasting efficacy
under field conditions. We evaluated under laboratory conditions the wash resistance of two
LLINs (PermaNet 1.0, Vestergaard-Frandsen, Denmark; Olyset, Sumitomo Chemical Co., Japan),
Updated March 9, 16
two candidate LLINs (Dawa, Siamdutch Mosquito Netting Co., Thailand; Insector, Athanor,
France) and a net treated with a process designed to increase its wash resistance and compared
them with conventionally treated nets (deltamethrin, 25 mg/m(2)). Nets of all six types were
washed using a standard protocol and tested weekly using WHO cone bioassays with Anopheles
gambiae (Kisumu strain). The PermaNet 1.0 was the most wash resistant with >50% mosquito
mortality in WHO cone bioassays after as many as 20 washes. The Dawa net also retained some
activity after repeated washing but exhibited wide variation in insecticide retention and
biological activity. The remaining nets lost >90% of their biological activity after six washes as
measured by 24-h mortality of A. gambiae in WHO cone tests. After 20 washes, all nets lost
>50% of their initial insecticide concentrations except for the Olyset net. After 20 washes, nets
were heated for 4 h at 60 degrees C to determine whether biological activity could be restored
by heat-assisted regeneration. Only the Olyset net was regenerated by heating, with average
mosquito mortality and knockdown in WHO cone tests rising to >90% after heating for 4 h at 60
degrees C. However, regeneration of the biological activity of Olyset nets that had been washed
three times did not occur at 30 degrees C or 35 degrees C after 12 weeks. The wash resistance
of these LLINs corresponded well to their retention of biological activity observed in a field trial,
suggesting that wash resistance may be a good predictor of the longevity of insecticidal activity
of LLINs under field conditions.
Gimnig JE, Lindblade KA, Mount DL, Atieli FK, Crawford S, Wolkon A, Hawley WA, Dotson EM.
Laboratory wash resistance of long-lasting insecticidal nets. Trop Med Int Health 2005,
10:1022-9
3.8 Experimental hut comparisons of nets treated with carbamate or pyrethroid
insecticides, washed or unwashed, against pyrethroid-resistant mosquitoes.
The efficacy against mosquitoes (Diptera: Culicidae) of a bednet treated with carbamate
insecticide [carbosulfan capsule suspension (CS) 200 mg/m(2)] was compared with four types of
pyrethroid-treated nets in veranda-trap huts at Yaokoffikro near Bouaké, Côte d'Ivoire, where
the malaria vector Anopheles gambiae Giles carries the kdr gene (conferring pyrethroid
resistance) at high frequency and Culex quinquefasciatus Say is also pyrethroid resistant.
Pyrethroids compared were lambdacyhalothrin CS 18 mg/m(2), alphacypermethrin water
dispersible granules (WG) 20 mg/m(2), deltamethrin 50 mg/m(2) (Permanet) and permethrin
emulsifiable concentrate (EC) 500 mg/m(2). Insecticidal power and personal protection from
mosquito bites were assessed before and after the nets were used for 8 months and hand
washed five times in cold soapy water. Before washing, all treatments except permethrin
significantly reduced blood-feeding and all had significant insecticidal activity against An.
gambiae. The carbosulfan net gave significantly higher killing of An. gambiae than all pyrethroid
treatments except the Permanet. Against Culex spp., carbosulfan was more insecticidal and
gave a significantly better protective effect than any of the pyrethroid treatments. After
washing, treated nets retained various degrees of efficacy against both mosquito genera - but
least for the carbosulfan net. Washed nets with three types of pyrethroid treatment
(alphacypermethrin, lambdacyhalothrin, permethrin) gave significantly higher mortality rates of
Culex than in huts with the same pyrethroid-treated nets before washing. After five washes, the
Updated March 9, 16
Permanet, which is sold as a long-lasting insecticidal product, performed no better than the
other nets in our experimental conditions.
Asidi AN, N'Guessan R, Hutchinson RA, Traoré-Lamizana M, Carnevale P, Curtis CF. Experimental
hut comparisons of nets treated with carbamate or pyrethroid insecticides, washed or
unwashed, against pyrethroid-resistant mosquitoes. Med Vet Entomol 2004, 18:134-40.